mctp: Avoid leak of mctp_sk_key

mctp_key_alloc() returns a key already referenced.

The mctp_route_input() path receives a packet for a bind socket and
allocates a key. It passes the key to mctp_key_add() which takes a
refcount and adds the key to lists. mctp_route_input() should then
release its own refcount when setting the key pointer to NULL.

In the mctp_alloc_local_tag() path (for mctp_local_output()) we
similarly need to unref the key before returning (mctp_reserve_tag()
takes a refcount and adds the key to lists).

Fixes: 73c618456d ("mctp: locking, lifetime and validity changes for sk_keys")
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Reviewed-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mctp/route.c

@@ -372,6 +372,7 @@ static int mctp_route_input(struct mctp_route *route, struct sk_buff *skb)
 			trace_mctp_key_acquire(key);
 
 			/* we don't need to release key->lock on exit */
+			mctp_key_unref(key);
 			key = NULL;
 
 		} else {
@@ -584,6 +585,9 @@ static int mctp_alloc_local_tag(struct mctp_sock *msk,
 		trace_mctp_key_acquire(key);
 
 		*tagp = key->tag;
+		/* done with the key in this scope */
+		mctp_key_unref(key);
+		key = NULL;
 		rc = 0;
 	}